Annealing furnace



Nov. 5, 1940- M. c. BATES EQTAL ANNEALING FURNACE 1938 2 Sheets-Sheet lFiled May 24 22 23 fizz/ 712K02 kTO STA C'K Nov. 5, 1940.

M. C. BATES ETAL ANNEALING FURNACE Filed May 24, 1938 2 Sheets-Sheet 2Patented Nov. 5, 1940 PATENT OFFICE ANNEALING FURNACE Mark C. Bates andBror Helgedin Stenberg, Chicago, Ill. said Stenberg assignor to saidBates Application May 24, 1938, Serial No. 209,715

Claims.

Our invention relates in general to furnaces, specifically furnaces fortreating metals, such as in the form of wire and the like, for thepurpose of annealing them.

5 When metals are formed by any of the usual processes such as drawing,rolling. casting, swedging or the like, strains are left in the metalwhich result in non-uniformity, or the metal as a whole ismetallurgically in an undesirable condition because of the hardnessresulting from breaking down the crystal structure when work isperformed on it. Improved manufacturing methods have made it possible toprocess the metal in a rapid succession of steps from the ore to thefinished article so that production is carried out in a fraction of thetime heretofore required. As has been stated many times, however,annealing operations still comprise a bottle neck in that the otherwisesmooth flow of metal articles from ingot to shipping floor is stillslowed up because of imperfect annealing methods and equipment. Amongthe principal problems in annealing, of course, are the time factor andthe cost element, but additional problems arise because of non-uniformapplication of heat which results in the production of a non-uniformproduct and scaling of the metal article, which produces an inferiorfinal result and often a large number of rejected parts. While ourinvention contemplates the improvement of annealing technique generally,it is principally concerned with improvements in annealing furnaces andassociated structures particularly suitable for annealing wire andsimilar articles but 36 also capable of use in still other annealingoperations.

The principal object of, our invention is the provision of improvedannealing equipment.

Another object is the more even application of 40 heat to metal articlesand the likeduring the process of annealing.

Another object is the provision of an improved furnace designparticularly suitable for use in annealing operations.

time usually required for annealing, decrease in over-all costs,including the amount of fuel employed, decrease in scaling, andproduction of a more uniform product.

Other specific objects and features of our invention will be apparentfrom a consideration of the following detailed description taken inconjunction with the accompanying drawings wherein Fig. 1 is anelevational view of an annealing Still further objects look to adecrease in the (Cl. 266-5Y furnace constructed in accordance with ourinvention, the figure being of relatively reduced size to conservespace,

Fig. 2 is a vertical sectional view taken through a furnace constructedin accordance with our invention and also illustrating the arrangementof the annealing pot within which the material is supported during theannealing operation,

Fig. 3 is a transverse sectional view taken along the line 3-3 of Fig.2,

Fig. 4 is a similar section taken along the line 4-4 of Fig. 2, and IFig. 5 is a sectional view shown in reduced scale showing a featureemployed for cooling the annealing pot and contents after they arewithdrawn from the furnace.

Generally considered, we produce a furnace of circular cross section andarranged to support an annealing pot in a vertical position within thefurnace so that substantially the entire outside surface of the pot isin contact with hot gases within the furnace. We employ a plurality ofrows of burners disposed around the furnace in such a manner as to firetangentially of the annealing pot, at least one row of burners firingagainst an imperforate breast wall. In the preferred design an uppercover is provided which is removable for insertion of the annealing .potand contents, and the exhausted gases from the burners are withdrawnthrough a lower central flue in order to produce a more even applicationof heat and generally provide a more desirable and convenient structure.The preferred method of heating the furnace is by the use of pre-mixedvaporized fuel and air produced by means of the apparatus and methodshown in French Patents Nos. 2,122,684 and 2,123,887, respectively. Theapparatus defined in the French patent is known to the trade under thename Vapofier. Pre-mixed or aspirated gas may be employed, however,without change in the design of the furnace, although the results arenot quite so satisfactory. The circular breast wall at the bottom of thefurnace prevents the flame from the burners from coming into directcontact with the annealing pot so as to cause uneven application ofheat, and also produces a swirling action of the exhaust gases which iscommunicated to substantially all of the body of gases within thecircular orifice between the annealing pot and furnace wall so that theflame from the upper row or rows of burners is also prevented fromcoming into direct contact with the annealing pot and local over-heatingis also prevented in the region of theupper burners. This is indicatedby the very unusual uniformity in the application of heat and also bythe fact that the annealing pot shows substantially no scaling such aswould occur if the flame were to be projected directly against it.

Referring now to the. drawings: we provide a circular side wall Ill,bottom II and removable top cover I2. of insulation l3 which may be firebrick or other suitable refractory material, a sheet metal outside coverI4, vertical supports it, and re-enforcing hoops l1. Naturally, thespecific construction of these parts may be modified in any suitable way.to provide a circular wall having suitable support and suitable heatinsulating properties.

The removable cover l2 comprises two frame members l8 and I9 nested asshown with a substantial layer of heat insulating material 2| betweenthem, the heat insulating material being preferably a usual type ofrefractory such as employed in furnace structures. Cross bails 22 areprovided with a loose lifting ring 23 for removing the cover vertically.An annular channel is provided at the top edge of the side wall bytheprovision of a channel member 24 which is suitably secured as bywelding to the metal support portions of the side wall. This channel isadapted to be filled with sand or other suitable sealing material, andthe projecting annulus of the member l9 by seating itself into the sandin the channel forms a seal which positively excludes air at thejointure between the removable cover and the side wall.

The metal to be annealed is supported within an annealing pot whichcomprises a material supporting member having an imperforate bottom 26and side wall 2'! and an imperforate inverted cover 28. As shown, theinverted cover rests within the hopper and a layer of sand or suitablesealing material 29 is provided to exclude air in the annular spacewhere the bottom of the inverted cover engages the hopper. A pluralityof lift bars 3! are secured to the hopper portion of the annealing potand are provided with top openings 32 in which a hook or suitableimplement may be engaged to lift the entire annealing pot out of thefurnace when the cover l2 has been removed. A lift ring 33 is providedon the upper end wall of the inverted cover 28.

A plurality of radial piers 34 are provided at the bottom of the furnaceon which the annealing pot rests, thereby furnishing a firm support butstill allowing ample space so that substantially the entire loweroutside area of the annealing pot may be swept with hot gases while theburners are in operation. As shown in Fig. 4, only some of the radialpiers are long enough to act as spacers for a circular breast wall 36,the center ones leaving still more space for the passage of hot gases.Blocks 3'! disposed between the outside of the breast wall and thefurnace wall also serve to position the breast wall 36. The piers 3 4the breast wall 36 and the blocks 31 are all carried on the furnacebottom and are all formed of suitable insulating material such asrefractory brick or the like.

In line with the breast wall 36 and substantially equally spaced aroundthe periphery of the furnace wall [8 we provide a plurality oftangential openings 38 within which burners 33 preferably of a highvelocity type are inserted. These burners fit snugly into the openings38 so as substantially completely to seal the 'open- The side wallcomprises a layer ings and prevent the admission, of secondary air. Asalready explained, a pre-mixture of fuel and air preferably is burned sothat there is no need for'the admission of secondary air to obtaincomplete combustion and the fuel mixture admitted is burnedsubstantially completely with unusual high efliciency. Suitable piping4| is employed for the delivery of combustible mixture to the burners,it being unnecessary to explain in detail the arrangement of the pipingas any suitable connections may be employed which will result in thedelivery of substantially uniform amounts of fuel and air mixture to theseparate burners.

Above the openings 38 and also tangentially arranged areadditionalopenings 42 containing burners 43. This arrangement issubstantially thesame as described in connection with the lower group of burners exceptthat the burners 43 do not fire against a breast wall but tangentiallydirectly into the annular space between the furnace wall andtheannealing pot.

The annealing pot obviously may contain any. suitable type of materialto which heat is to be applied. 'In an installation heretofore employedthe furnace has been employed for annealing wire with veryunusualresults and in orderto completely illustrate one application of ourinvention we show more or less schematically a charge of wire as it ispreferably carried within the annealing pot. A standard 44 is providedon which coils of wire 46 are stacked, a base being provided on thestandard for supporting it upright. The base is so dimensioned as to bespaced somewhat away from the inside wall of the portion 21 of thehopper, and'preferably it is this space in this form of installationwhich is filled with sand for sealing the connection between theinverted cover 28 and the supporting member which .together comprise theannealing pot. The standard is provided with an opening near the top forthe engagement of a book or other suitable tool whereby when theannealing pot is removed from the furnace and the inverted cover 28taken off, the entire charge of wire may be removed.

The temperatures at which materials are annealed vary somewhat dependingupon the nature of the product and so in the further description of ourinvention we shall consider the application of heat to wire so that thewire will be at the preferred annealing temperature, namely 1200 degreesF. When wire is heated to this temperature it cannot be removed imme-.diately from the furnace or scaling will result and also strains will beproduced because of unequal cooling. When the annealing operation hasbeen completed, thewire, of course, may be allowed to cool in thefurnace, but for production purposes it is advisable to remove the wirefrom the furnace as soon as possible so that another charge may beintroduced. For this purpose we provide a separate insulating cover 48arranged to provide a seal in an annular recess 49 in a floor 5! whichcomprises a heat insulating medium such as fire brick. The annealing potwhich we indicate more or less schematically at 52 is withdrawn from thefurnace, placed centrally of the annular recess 49 and the insulatingcover 48 immediately placed over it. This arrangement retains the ,heatso that the wire may cool slowly and uniformly and substantially theidentical results obtained as if the annealing pot and contents wereallowed to remain in the furnace during cooling.

The manner of charging the furnace and firing it are believed obviousfrom the preceding description. In actual, operations we have placedtemperature recording devices in various places in the annealing pot andon the outside of the annealingpot but within the furnace and have founda remarkable result to be obtainable. In the first place, taking thetemperature within the furnace but outside of the annealing pot when thedesign was to anneal wire at 1200 degrees F. showed that the temperaturewithin the furnace but outside the annealing pot was only 1210 degreesFl, that is, a' temperature drop of only 10 degrees across the wall ofthe annealing pot. Furthermore, the temperature found within theannealing pot was of uniformity such that no measurable temperaturevariation was found to exist anywhere; that is to say, within the limitsof accuracy of the best measuring instruments available for the purpose,the temperature was absolutely uniform at 1200 degrees F. during theannealing operation.

We further found that complete annealing was obtained of a charge of twotons of wire insix hours using only thirty-three gallons of oil percharge. This is contrasted with the best previous results obtained on.acoal fired furnace employed heretofore for a given operation because ofthesupposed advantages of uniformity and low cost obtained with coal. Inthe coal fired furnace twelve to fifteen hours was required to carry onan annealing operation and 1500 pounds of very high grade coal wereemployed, so that the actual cost of fuel when employing oil was in theneighborhood of of the cost of coal. Furthermore in the coal firedoperation the annealed wire showed a'20% variation whereas the wireannealed. by means of our invention showed substantially no variationwhich could be measured on the usual equipment employed for testpurposes. Another advantage in our furnace is that the annealing pot isnot scaled, appreciably, even at the point where the top row of burnersis fired without the use of a breast wall. Thus, the'pot life isincreased tremendously, a uniform product obtained and the proportion ofrejected products resulting from scaling, non-uniformity and the like isreduced to practically zero.

The unusual uniformity obtained in heating the wireor other metalarticles which may be supported in the annealing pot is unquestionablydue, in large part, to the uniform movement and distribution of hotgases within the'furnace and the fact that substantially the entireoutside surface of the annealing pot is swept continuously by thesegases. The piers which support the annealing pot engage only arelatively small proportion of the bottom thereof, but on account oftheir position and the movement of the gases these piers aresubstantially of the same temperature as the hot bases, that is to say,they certainly are not at a relatively hightemperature such as to causelocal heating where they engage the pot.

The tangential arrangement of the bottom row of burners so positioned asto direct their flames against the outside circumference of the breastwall and the fact that the gases in expanding can only escape upwardlyfrom the channel-like recess between the furnace wall and breast wall,produces a rapid swirling and generally upward movement of the exhaustgases which apparently persists at least as far upwardly as the top rowof burners because no evidence can be found that the flame from the toprow of burners actu-- ally impinges against the outer surface of theannealing pot. We have not determined in detail the path of the gases asthey move upwardly and then downwardly again to pass out through thecentral bottom flue but theoretical calculations and investigations showclearly that the gases rise in a swirling or spiral fashion and thatthere is a movement of gases over substantially the enetire outersurface of the annealing pot. That this is clear is evidenced partly bythe fact that only the bottom row of burners may beemployed withsubstantially equivalent results as the two rows particularly if theheight of the furnace be decreased somewhat. The additional top row ofburners, however, does result in greater uniformity in a relatively highfurnace, and if the height is still somewhat further increased it ispossible to increase the number of rows of burners providing they arepositioned so that the swirling movement of the gases will continue tohave the efiect'of keeping the flame therefrom out of contact with theannealing pot.

Shaping the furnace in the form of a truncated cone apparently hascertain advantages in maintaining uniformity of heating as well asimparting greater rigidity from a structural standpoint. Whilesubstantially vertical side walls may be employed, we prefer to use thesloping type as shown.

The furnace of our invention may be built in different sizes providing,of course, that the size be not decreased or increased to such an extentthat the same relative performance may not be.

obtained. Friction tending to restrain the movement of hot gases in themanner described, must be taken into consideration and also certainaspects of practicability as those skilled in the art will understand.That our disclosure may be complete in this respect, however, we wish topoint out that we have obtained very good results with a furnacestanding approximately nine feet from the floor with the otherdimensions in proportion, substantially as shown in the drawings and inwhich the annealing pot carries a charge of approximately two tons ofmetal.

We employ the term, ftangential to define.

the position of the burners notwithstanding the fact that the burnersare not directly tangential to eitheri the furnace side wall, the breastwall or the annealing pot, although as clearly shown in Figs. 3 and 4,the flame projected by the burners is substantially generally tangentialto the breast wall at the bottom row of burners and the annealingpot atthe upper row of burners.

What we claim as new and desire to protect by Letters Patent of theUnited States:

1. In an annealing furnace of the character described,a circular sidewall, a furnace bottom having a flue therein, a removable cover, meansincluding a plurality of piers for supporting an annealing pot so as topermit circulation of hot breast wall and hot combustion gases have awhirling motion imparted thereto, and a second row ofburners projectingtangentially through said furnace wall above said breast wall insubstantially the same direction as said first-mentioned row of burners,whereby combustion gases from said second row of burners have a whirlingmotion imparted thereto at least in part by the movement of combustiongases from said firstmentioned row of burners, and whereby the secondrow of burners are prevented from locally overheating the annealing pot.

2. In an annealing furnace of the character described, a circularfurnace side wall having the general outline of a truncated cone, a topcover adapted to be removed to allow insertion of an annealing pottherein, means for sealing said cover and side wall, a bottom having aflue therein, an annealing pot adapted to contain metal articles, saidpot being of generally cylindrical shape and having smaller outsidedimension than minimum inside dimensions of the furnace body, means forsupporting said annealing pot within said furnace out of contact withinside side, botv tom and top surfaces thereof so that substantially theentire outer surface of said annealing pot is, exposed tov furnaceatmosphere, a circular breast wall disposed between said annealing potand circular furnace wall, and a plurality of rows of burners projectingnon-radially through the circular furnace wall, at least one of saidrows of burners being in line with said breast wall whereby to impart aswirling motiomto all of the hot gases between the outside annealing potsurface and the inside surface of the furnace.

3. In an annealing furnace of the character described-a circular furnaceside wall having the general outline of a truncated cone, a top coveradapted to be removed to allow insertion of an annealing pot therein,means for sealing said cover and side wall, a bottom having a finetherein; an annealing pot adapted to contain metal articles, said potbeing of generally cylindrical shape and having smaller outsidedimension than minimum inside dimensions of the furnace body, means forsupporting said annealing pot within said furnace out of contact withinside side, bottom and top surfaces thereof so that substantially theentire outer surface of said annealing pot is exposed to furnaceatmosphere, a circular imperforate breast wall seated on the bottom ofthe furnace between the side wall of the furnaceand said annealing pot,a plurality of burners projecting through the side wall of the furnaceso as to direct their flame tangentially of the breast wall, and asecond row of burners positioned above said first-mentioned plurality ofburners in a position to direct their flames substantially tangentiallyof the outside wall of the annealin pot and in substantially the samedirection as said first mentioned row of burners, said breast wallimparting a swirling motion to exhaust gases from the bottom burners,and said swirling motion of the gases preventing the flame from theupper burners coming into such direct contact with the annealing pot asto cause local overheating thereof.

4. In anannealing furnace, a circular side wall, a furnace bottom havinga central flue therein, a circular breast wall lying on the bottom ofthe furnace and spaced from said side wall, a plurality of piers restingon the furnace bottom within said breast wall and radially disposed withrespect to said flue, an imperforate sealed annealing pot of circularcross section, a removable cover whereby said annealing pot may beinserted vertically and set on said piers, said annealing pot beingspaced from the bottom, top, and side walls of the furnace, a row ofburners extending through the furnace wall in position to firetangentially against said breast wall, a second row of burners above thebreast wall set tangentially to flre into the space'between the furnacewall, 20

and annealing pot, and means for delivering a combustible mixture of airand oil vapor to said burners.

5. In an annealing furnace, a circular side wall, a furnace bottomhaving a central bottom flue therein, a circular breast wall lying onthe furnace bottom and spaced from said side wall, a

plurality of piers resting on the furnace bottom between said breastwall and said central bottom flue, the upper surface of said piers onwhich an annealing pot rests being only slightly below the upper limitof said breast wall, an imperforate sealed annealing pot of circularcross section resting on said piers so that substantially the en-.

tire annealing pot'projects above said breast wall,

a removable cover for the furnace whereby said annealing pot may beinserted vertically and set on said piers,- said annealing pot beingspaced from the breast wall to allow an annular opening for the passageof hot gases to the flue, and

the annealing pot being spaced from the bottom,

side wall and cover whereby substantially the entire outside surfacethereof may be in contact with the furnace atmosphere, and a pluralityof burners projecting tangentially through said furnace wall to fireinto the space between the furnace wall and side wall of the annealingpot,

' at least a major proportion of said burners being MARK c. BATES. B.masons STENBERG.

